Porous Janus polymer single crystals via liquid-liquid phase separation at oil-water interface

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Coupling liquid–liquid phase separation (LLPS) with crystallization has emerged as an effective strategy for regulating polymer crystalline structures and elucidating crystallization mechanisms. In this work, we investigate the evaporative crystallization of poly(caprolactone) at water surface using three PCLs with different chain-end functionalities. By tailoring the chain ends and employing evaporative crystallization on water surfaces, the crystallization pathways were systematically controlled, enabling the formation of single-crystalline porous Janus films and two-dimensional (2D) Janus polymer single crystals. The observed structural evolution is attributed to the interplay between LLPS and crystallization during solvent evaporation. These results reveal a strong correlation between polymer chain conformation and crystalline morphology at liquid–liquid interfaces, providing new insights into interfacial polymer crystallization and the design of anisotropic polymeric structures.